Subtraction method for NLO corrections in Monte-Carlo event generators forleptoproduction

In the case of the gluon-fusion process in deep-inelastic leptoproduction, I explicitly show how to incorporate NLO corrections in a Monte-Carlo event generator by a subtraction method. I calculate the parton densities to be used by the event generator in terms of (MS) over bar densities. The method is generalizable. A particular motivation for treating the gluon-fusion pr ocess is to treat diffractive deep-inelastic scattering properly, since in diffractive scattering the gluon density dominates the quark densities. I a lso propose a modified algorithm for treating parton kinematics in event ge nerators; the new algorithm results in much simpler formulae for the NLO co rrections. A disadvantage of the new method is that some of the generated e vents may have negative weights. However, an adjustable cut-off function is present in the formalism, and this permits a renormalization-group-like tr ansformation that can be used to at least reduce the proportion of events w ith negative weights.